Combustion-powered, fastener-driving tools, such as combustion-powered, nail-driving tools and combustion-powered, staple-driving tools, are exemplified in Nikolich U.S. Pat. No. Re. 32,452, Nikolich U.S. Pat. Nos. 4,522,162, and 4,483,474, Wagdy 4,483,473, and Nikolich 4,403,722.
Typically, such a tool comprises several normally opened switches connected to a battery, namely an on-off switch, a head switch, and a trigger switch, all of which must be closed to enable ignition of a combustible fuel in a combustion chamber of the tool. The on-off switch is closed by the user pressing a lever, which is mounted operatively to a handle of the tool, with the palm of one hand and is used to control a fan. The head switch is closed by pressing a workpiece-contacting element, which is mounted operatively to a nosepiece of the tool, firmly against a workpiece. The trigger switch is closed by pulling a trigger, which is mounted operatively to the handle, with the index finger of the same hand. Typically, in such a tool, the head and trigger switches are interlocked mechanically in such manner that the trigger switch cannot be closed unless the head switch is closed.
Heretofore, in the ignition system of such a tool, it has been known to use a battery for powering the ignition system, to use a charge-pump oscillator to charge a capacitor over a timed interval, and to cause a sudden discharge of the capacitor through the primary winding of a transformer, when the timed interval ends, so as to produce a spark at the spark gap of a spark plug connected to the secondary winding of the transformer. Although such a system has proved to be quite satisfactory, some variations can occur from one operation of the tool to another, particularly if the battery voltage drops below a minimum voltage needed for proper ignition when the fan is enabled or if the capacitor is not charged to a minimum voltage needed for proper ignition over the timed interval. Even if the tool continues to operate satisfactorily, a user may be nonetheless able to perceive such variations, which are reflected directly in combustion efficiency and indirectly in perceived recoil of the tool. Any significant variations in perceived recoil of the tool can be distracting to a user.
Recently, photoelectric switches that can be advantageously used as the head and trigger switches of such a tool have become available, as disclosed in a copending patent application assigned commonly herewith and filed Jun. 17, 1991, under U.S. Ser. No. 07/716,215, for PHOTOELECTRIC SWITCH SEALED AGAINST INFILTRATION OF CONTAMINANTS. Thus, a need has arisen for an ignition system in a combustion-powered tool, such as a combustion-powered nail-driving tool or a combustion-powered, staple-driving tool, enabling such photoelectric switches to be effectively used as the head and trigger switches. This invention is addressed to the need that has arisen.